Diaphragm for electrolysis.



0. DIBWENBACH.

DIAPHRAGM POR ELEoTRoLYsIs. APPLICATION IILB) JULY 1, 1911.

Patented sept. 24,1912.

OTTO DIEFFENBACH, OF DARMSTADT, GERMANY.

DIAPHRAGM FOR ELECTROLYSIS.

Specification of Letters Patent.

Patented Sept. 24, 1912.

Application led July 1, 1911. Serial No. 636,368.

improved porous diaphragm for the pur-I pose of electrolysis.

Porous diaphragms are required :for use in very different ways for electrolysis, e. g. electrol'yzing salt solutions, when the diaphragms are so inserted in the vais that liquid is at both sides of them.` During electrolysis the liquid frequently rises considerably higher on the one side than on the other so that there is a very considerable pressure on the diaphragm when the vat is large; to withstand the breaking strain the diaphragm must have considerable strength. For this reason the diaphragms must be made fairly thick because the porous substances of Which they consist have per se no great strength to withstand breaking strain. By so makinA them, however, the electrical resistance o the plates is considerablywincreased causing loss ot' energy' whichzis quite appreciable when working on a large scale.

A primary object of my invention is to remedy this defect, Accordingly Y[ use as a diaphragm 'for the purposes ot' electrolysis a plate of asbestos and cement in which the asbestos fibers are positioned approxiu'iately parallel with the plane of the plate. Such plates areobtained, as is known, when cement and asbestos fibers are worked up in suitable proportions on a machine for making paper or pasteboard, or on another machine for operating according to a similar principle, so that the asbestos fibers are placed parallel to one another and 'Form a layer into which the particles of cement are introduced. The parallel arrangement of the asbestos fibers in the direction of the plane of the plate gives such plates great ability to withstand breaking strain so that they can be made very thin and the electrical resistance be consequently reduced. Sufficient porosity can be obtained either by not pressing the plates at all or only slightly while they :harden or by adding to them during their manufacture substances,

as e. g. mineral salt, which may be washed outl later.

ln the accompanying lrmvings Figure 1 a vertical section through a plate accordlng to my invention, whereas Fig. 2 isa vertical section through a vat showing such a plate used as a diaphragm when electroiyzing a salt solution, and Fig. 3 is a like view of one form of machine which may be used for making my diaphragms. I

ln Fig. l, adesignates the plate composed ot' 4eenient and having in it asbestos fibers L positioned so that they are substantially parallel with the plane of the plate. Such plates. which are made without-pressure while they harden, have a very great ability to withstand breaking strain and a small electrical resistance and are consequently very suitable as diaphragms.

Fig. 2 represents the electrolysis of a solution ot' potassio chlorid (KCl) for obtaining potassium lye (KOI-l). l is the vat which contains the potassio chlorid solution and in which the cement plate a (Fig. 1) having asbestos fibers b is inserted t'orinr ing the diaphragm. Potassium is obtained at electrode Q and chlorin at electrode 3.

.The potassium forms with .the water potassium lye (KOH) and this is drawn oit' through a stop cock 4, from time to time as soon as it is sufficiently concentrated. A considerable lateral pressure is produced each time on the diaphragm as the compartment containing electrode 3 is always kept filled and therefore the diaphragm must be well able to witlistandbreakingstrain.

Fig. 3 illustrates a known process by means of which an asbestos-cement plate having asbestos fibers parallel with the plane ot the plate can be made, (compare, e, g.-

layer and onto the sur-face of the asbestos,

mixture in the vat.- 'lhe particles of cement lodge between the asbestos fibers and envelop these. The cement-asbestos layer or web 1s (caa nor.T pressed by roller 1G on an endless belt ll, wound up in known manner on another roller, not shown, until it is sufiiciently thick, is then removed and straightened so that it forms a plate. It is then left to harden while not pressed at all or only very slightly, whereby the diaphragm is obtained. lt` may be remarked that this process o1e Ymaking the plates is described merely by way of example. Every process 'can be used by which cement-asbestos plates having tibers placed parallel with the plane of the plate can be produced, as, for example, the process desc-ribed in the United States Letters Patent to Hatschelr, 7 69,07 8 dated August 30, 1901i. 'lllieV plates may not be pressed so severely, however, is necessary when they are to be used as rooiing tiles, because otherwise they lose much ot' t-heir porosity. lt may be further remarked that cement and asbestos have been employed heretofore for manufacturing' diaphragme. rThese have, however, always been made by mixing cement and asbestos with water and placing the mixture into suitable molds Which determine the final shape.' ln this manner no denite positioning; of the asbestos fibers-parallelto the plane oi' the plate-could be obtained: on the contrary the fibers were placed irregularly in the cement and therefore gave the plate no ability to withstand breaking strains. Such an ability can only be obtained, on the contrary, when the diaphragm is made with the aid of one of the known processes by which the asbestos fibers are positioned parallel with one another and with the plane of the plate, such as processes for manufacturing roofing tiles or plates which have already been proposed.

Comparative tests have shown that plates l0 mm. thick composed of 8O parts of cement and 520 parts of asbestos made on the pasteooard machine and hardened without pressure stood, in spite of an electrical refess by about 25%, more than twice the load before they broke than plates which were inade by simply mining cement and asbestos in the above proportions andtillingthe mixture into suitable molds. .Obviousl v,

the reason is that, in consequence of the horizontal position of the fibersy and the attachnient of the saine occasioned thereby when made on the pasteboard machine, the plates are elastic and bend slightly vwithout tracturiiig, whereas the plates made by simply mining and casting the raw materials are .brittle and when severely loaded fracture directly without bending.` In comparison with plates ot equal dimensions and ma'le of cement and sodium chlorid they stand about 1g; times as much as those made of cement, sodium chlorid and hydrochloric acid, z. e. almost twice the load. This possibility ot' greater load is exceedingly important in practice, however, because it admits of the plates themselves and the entire apparat-us being made considerably larger than when the plates are weaker.

The asbestos-cement plates in question become considerably stronger when they are subjected to slight pressure after being shaped. lt is true that this increase in strength is obtained at the cost of porosity,

for which reason the pressure may only be slight if the electrical resistance is not to increasatoo much. On the other hand, such pressed plates can be made thinner and thereby 'the increase in electrical resistance can be wholly -or partiallyV equalized. An`

increase in porosity can be obtained in nonpressed and also in pressed plates by mixing with the cement before the plates are shaped such substances which can be removed by dissolving them out or in other manner after the plates have been hardened.

lclaim:

l.V A porous diaphragm, 'for the purposes ot electrolysis, composed of an intimate mixture of cement and asbestos iibers'saidtibers being located parallel with the plane of the diaphragm.

The hereindescribed process ot' manufacturing porous diaphragms, tor the purposes ofelectrolysis, which consists in mifring asbestos .Fibers with water, in removing said libers from the water and applying cement to the ibers and simultaneously forming the fibers and cement into a platehaving' the asbestos fibers located therein parallel to the plane of the plate, and in allowing the plate to dry.

3. The hereindescribed process ot lecturing porous diaphragms, tor the pur.- poses ot electrolysis, which consists in mixingr, asbestosiibers with water, in removing said fibers from the water and simultanen ously applying; ceinept to the bers and'simultaneously forming the fibers and cement JEAN GRUND, CART. GRUND. 

